So this started at the beginning of last week with a report from a member of teaching staff experiencing really low Internet speeds while browsing via Wi-Fi with an Intel Dual Band Wireless AC-3165. Connected via LAN gave consistent download speeds of > 80Mbps but switch to Wi-Fi and they got barely 0.02Mbps.
UPDATE: 05/02/2021 – This has also been seen to fix slow Wi-Fi issues on Intel(R) Wi-Fi 6 AX201 160MHz series NICs.
After many hours trawling through Event Viewer and changing, testing and changing back advanced Wi-Fi settings I came across “Receive Segment Coalescing” see https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2012-r2-and-2012/hh997024(v=ws.11).
Disabling this setting on the network card resolved the issue first time, however it didn’t explain why the laptop had been working for 5 months previously without issue.
After another 3 hours of investigation I found that a recent installation of SonicWALL Global VPN Client must be causing the issue as having remove this and re-enabled Receive Segment Coalescing the issue was no where to be seen.
Steps to disable Receive Segment Coalescing manually on the Intel Dual Band Wireless-AC 3165 :
1) Open an Admin Command Prompt window:
Start > All Apps > Windows System -> Right-click “Command Prompt” > More > Run as administrator
2) Get your network adapter name:
3) Note your adapter’s name, mine was called “Wi-Fi”
4) Get your network adapter “Receive segment coalescing” (Rsc) settings:
5) Disable Rsc for your network adapter:
powershell Disable-NetAdapterRsc -Name Wi-Fi
6) Verify Rsc is disabled for ipv4 and ipv6, on your network adapter:
7) Re-test your wireless internet connection.
An additional workaround for this is also to set the MTU for the Wi-Fi to 1400 instead of the default 1500
Change MTU to 1400
To VIEW your MTU:
Right Click Start > Command Prompt (Admin) > Type or right-click-paste the following command:
netsh interface ipv4 show subinterfaces
To CHANGE your MTU to 1400:
netsh interface ipv4 set subinterface “W-Fi” mtu=1400 store=persistent
UPDATE: 03/12/20 – I have recently found that you can also disable DNE Light Weight Filter and QoS Packet Scheduler settings which has the same effect.